Conditions Conducive to Forming Crystalline Uranyl Silicates in High Caustic Nuclear Waste Evaporators

Technical Report · Tue Nov 16 04:00:00 EST 2004

DOI:https://doi.org/10.2172/835626· OSTI ID:835626

OJI, LAWRENCE

The laboratory conditions used to synthesize the uranyl silicate minerals are almost identical to the evaporator conditions under which high caustic nuclear wastes are processed to reduce total liquid waste volume. The only significant difference lies in the sodium ion concentration in such caustic nuclear wastes, which typically averages around 5.6 M Na+. In this investigation, synthetic uranyl silicate minerals (sodium weeksite, sodium boltwoodite and uranophane) were produced only under low Na+ concentration (less than 0.02 M), while attempts to synthesize these same uranyl silicates minerals in the presence of high Na+ concentration (high ionic strength reacting media), which is typical of caustic nuclear waste evaporator processing conditions proved unfruitful. In the presence of high Na+ concentration the main product for the same soluble silica-uranium reaction mixture shifts towards the formation of mainly clarkeite (Na[(UO2)O(OH)](H2O)0-1), a hydrated sodium uranate and not to wards the formation of uranyl silicates. Thus, the presence of high Na+ concentration in the reaction mixture of dissolved uranium and silica inhibits or suppresses the formation of crystalline uranyl silicates. We therefore conclude that evaporator fouling by uranyl silicate minerals is not easily produced under nuclear waste processing conditions because of the high Na+ concentration in the liquid wastes.

• Research Organization: Savannah River Site (US)
• Sponsoring Organization: US Department of Energy (US)
• DOE Contract Number: AC09-96SR18500
• OSTI ID: 835626
• Report Number(s): WSRC-MS-2004-00823
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
CLARKEITE
EVAPORATORS
FOULING
HIGHLY CAUSTIC NUCLEAR WASTE: SYNTHETIC URANYL SILICATE MINERALS
LIQUID WASTES
MIXTURES
PROCESSING
RADIOACTIVE WASTES
SILICA
SILICATE MINERALS
SODIUM IONS
SODIUM URANATES
URANIUM MINERALS
URANOPHANE
URANYL SILICATES